1. Field of the Invention
The present invention relates to a tank cap mounted over a liquid supply port in a tank for storage of a liquid such as fuel, and more particularly to an improvement in such a tank cap, comprising an outer cap element, an inner cap element fitted into the outer cap element, and a separator which is interposed between the outer and inner cap elements to divide a space between the outer and inner cap elements into an upper breather chamber communicating with the outside of a tank and a lower breather chamber communicating with the inside of the tank, and which has a communication bore permitting communication between the upper and lower breather chambers, so that the flowing-out of a liquid in the tank to the outside is inhibited, while permitting the breathing of the tank.
2. Description of the Related Art
Such a tank cap is already known, as disclosed, for example, in Japanese Utility Model Application Laid-open No.63-7664.
In a conventional tank cap, a communication bore permitting communication between the upper breather chamber and the lower breather chamber and the inner breather bore opening into the lower breather chamber are merely disposed vertically with the lower breather chamber interposed therebetween. Therefore, when the liquid in the tank rushes through the inner breather bore into the lower breather chamber, the amount of the liquid entering through the communication bore into the upper breather chamber is relatively large, and the damping function of the lower breather chamber for the liquid entering thereinto is not sufficient.
The present invention has been accomplished with such circumstance in view, and it is an object of the present invention to provide a tank cap wherein the damping function of the lower breather chamber against the liquid entering thereinto can be enhanced to effectively inhibit the flowing of the liquid from the lower breather chamber into the upper breather chamber.
To achieve the above object, according to a first aspect of the present invention, there is provided a tank cap comprising an outer cap element, an inner cap element fitted into the outer cap element, and a separator which is interposed between the outer and inner cap elements to divide a space between the outer and inner cap elements into an upper breather chamber communicating with the outside of a tank and a lower breather chamber communicating with the inside of the tank, and which has a communication bore permitting the communication between the upper and lower breather chambers. An auxiliary separator is connected to the separator to divide the lower breather chamber into a lower central chamber section communicating with the inside of the tank, an upper central chamber section which is disposed immediately above the lower central chamber section and into which the communication bore opens, and an annular chamber section surrounding the upper and lower central chamber sections. The auxiliary separator is provided with an upper transverse bore permitting communication between the upper central chamber section and the annular chamber section, and a lower transverse bore permitting communication between the lower central chamber section and the annular chamber section.
With the first aspect, even when a wave of liquid in the tank is formed, and a portion of the liquid rushes into the lower central chamber section in the lower breather chamber, such liquid hits against a ceiling wall of the lower central chamber section with its wave energy damped. In addition, the lower transverse bore and the upper transverse bore are disposed in positions displaced at least vertically from each other, so that the liquid entering from the lower transverse bore into the annular chamber section scarcely reaches the upper transverse bore. Further, the upper transverse bore and the communication bore open into the upper central chamber section from different directions displaced from each other through 90xc2x0, so that wave energy of the liquid entering from the upper transverse bore into the upper central chamber section is damped before reaching the communication bore. Thus, the lower breather chamber can exhibit a high damping function to effectively inhibit the movement of the liquid to the upper breather chamber to reliably prevent the flowing-out of the liquid to the outside of the tank cap.
According to a second aspect of the present invention, in addition to the first feature, the upper central chamber section has a bottom surface formed as a conical convex surface declined toward the upper transverse bore.
With the second aspect, the liquid with its wave energy damped in the upper central chamber section can be guided toward the upper transverse bore by the conical convex surface provided on the bottom surface of the upper central chamber section, and passed via the annular chamber section quickly back into the tank.
According to a third aspect of the present invention, in addition to the first or second aspect, each of the separator and the auxiliary separator is made of a synthetic resin; a first annular projection is formed on an outer peripheral surface of the separator to come into close contact with an inner peripheral surface of the inner cap element; a second annular projection is formed at an upper end of the separator to come into close contact with a ceiling wall of the outer cap element; and a third annular projection is formed at a lower end of the auxiliary separator to come into close contact with a bottom wall of the inner cap element.
With the third feature, the separator as well as the auxiliary separator and the outer cap element as well as the inner cap element can be sealed from each other without use of exclusive sealing members, leading to the simplification of the arrangement.